The present invention relates to paperboard laminates, and more particularly to a non-foil paperboard laminate useful for making containers for products such as fruit and citrus juices, beverages and the like as well as non-liquid dry products, wherein the laminate has good oxygen barrier characteristics as well as the ability to protect the products packaged therein against the loss of essential oils, flavor and vitamins.
Paperboard coated with low-density polyethylene (LDPE) has been used to make beverage containers, but falls short in providing an acceptable container. In particular, paperboard coated with LDPE has a relatively high permeability to oxygen which may lead to loss of flavor components and vitamins through oxidation. Flavor loss can also occur as a result of migration or uptake of flavor components into the LDPE layer, a process referred to as "scalping." Additional barrier materials have therefore been investigated to achieve the desired goal.
The oxidative loss of the vitamin C can be substantially reduced by the use of a laminate containing a metal foil as a liner along the interior of the container. However, the economics involved in using a metal foil preclude this solution from being a viable alternative. A search for economical alternatives to foil has resulted in the development of laminate structures utilizing coextruded polymer materials such as polypropylene, polyvinylidene chloride (PVdC) and ethylene vinyl alcohol copolymer (EVOH) as the barrier material. See, for example the Tanner U.S. Pat. No. 4,988,546, the Gibbons et al. U.S. Pat. Nos. 4,789,575 and 4,701,360, the Thompson et al. U.S. Pat. No. 4,513,036, and the Huffman U.S. Pat. No. 5,059,459.
In addition to being less expensive than foil-containing structures, paperboard laminates containing such barrier materials may exhibit superior flavor loss properties due to the use of lower levels of LDPE as the product contact layer. Many conventional commercial structures for a paperboard carton for juice and similar products now utilize a laminate containing ethylene vinyl alcohol copolymer as a barrier to oxygen and flavor oils.
Nylon has also been proposed and used commercially as a barrier polymer in plastic bottles (see Plastics World, February 1986, pp. 36-38), as a plastic packaging material (Aseptipak 84, pp. 119-148), and as a replacement for cellophane (Plastics World, July 1984, pp. 42-47). The properties of a barrier material used in plastic bottles or for packaging, however, are quite different from those required for a paperboard container and barrier materials useful in plastic bottles or wrapping material may not be useful for a barrier in a paperboard container. For a paperboard container, the Whillock et al. U.S. Pat. No. 3,972,467 discloses a nylon film laminated to a paperboard substrate by a low density polyethylene layer and having a low density polyethylene product contact layer. In this case, the nylon film is specified as having a tensile strength at the yield point of more than 4000 psi and an elongation at fracture of greater than about 200%. Such laminated film structures are expensive and require complex laminating equipment and the use of such high strength materials causes difficulty in the cutting of container blanks from a web of barrier board material and in the forming of the container.
The Thompson et al. U.S. Pat. No. 4,777,088 discloses a barrier board structure for flavor oil and oxygen retention in a juice carton wherein an extruded nylon layer of unspecified composition and physical properties is combined with a layer of a special ionic copolymer material sold by duPont under the trade name Surlyn on one or both sides. As described in U.S. Pat. No. 4,777,088, Surlyn is a necessary constituent of the described nylon barrier board laminate structure.
The Brown et al. U.S. Pat. No. 4,753,832 discloses a barrier based structure which has a product contact barrier layer of glycol modified polyethylene terephthalate (PET-G) and may also have a nylon oxygen barrier layer, but that patent does not disclose any specific type of nylon or specify desirable properties of the nylon material. As described in U.S. Pat. No. 4,753,832, PETG is a necessary constituent of the described barrier board laminate structure.
The Gibbons et al. U.S. Pat. No. 4,921,733 discloses various Nylon 6, Nylon 11 and Nylon 12 polymers, which are crystalline materials, having tensile strength of 10,000 psi or more, as abuse-resistent layers for use in combination with a caulking polymer such as a Surlyn ionomer resin and an oxygen barrier such as aluminum foil for paperboard containers.